There is a need for lightweight, structural panel arrays in sensor platforms, such as the AWACS, Predator, and other unmanned air vehicles. Many such aerospace applications require that the antenna be built onto the skin of the sensor platform, thereby requiring an exposed surface, or face, of the antenna aperture to be conformal or curved. Such conformal panel arrays require variable height radiating aperture since the backside electronic panels are typically planar. Also, as structural members, such arrays require load-bearing apertures.
It is generally desirable that aperture performance be maintained over a wide bandwidth and a wide scan range (e.g., a 40% bandwidth and a 60-degree conical scan). One of the difficult challenges in constructing such variable height antenna apertures is that anomalies are introduced into the array performance, at least in part, due to surface waves generated and supported by such a curved aperture. As individual radiating element of such a conformal array radiate electromagnetic energy, at least a portion of the energy is typically directed towards the backplane. This situation results in reflections of the electromagnetic waves, with implications to performance parameters, such as the radiation pattern and efficiency (e.g., variations to driving point impedance, which lead to increased return loss). Such effects can be compensated for, at least to some extent, for single radiator embodiments, or arrays with uniform antenna height above the backplane. A serious complication, however, in dealing with conformal arrays is that the various radiating elements are each disposed at different heights adding a multi-dimensional complexity. Consequently, such conformal arrays may operate with restrictions or undesirable constraints to parameters, such as radiation pattern performance (e.g., gain, side lobe suppression, beam widths) and bandwidth (e.g., return loss, VSWR).
One solution uses a faceted approach, in which both the aperture and the array electronics are locally planar, with portions of the array being displaced from a common plane according to the desired array profile. Another approach requires that the entire aperture and array electronics each be curved in a similar manner, so that the radiating elements effectively “see” a constant ground plane height. From an aperture design standpoint, aperture can be treated as a circular or cylindrical array. Either category of approach adds complexity to the overall antenna assembly design, as electronic modules and other components associated with such arrays must be housed according to complicated geometries.